Panel with light permeable images

ABSTRACT

A panel includes a sheet of light permeable, preferably optically clear transparent material and a transparent or translucent design superimposed on or forming part of a transparent or translucent base pattern. The design is visible from one side of the panel and a mirror image of the design is visible from the other side of the panel when a sufficiently high level of illuminated is provided on either side or both sides of the panel.

This application is the national phase of international applicationPCT/GB97/00020 filed Jan. 6, 1997 which designated the U.S.

FIELD OF THE INVENTION

This invention relates to panels and more particularly light permeablepanels that are partially imaged with at least one design that is alsolight permeable.

The term “light permeable” as used herein includes transparentmaterials, translucent materials and perforated materials. Transparentmaterials may have two parallel, plane surfaces or otherwise allowclarity of vision through the panel material, enabling the eye to focuson objects on the other side of the material and provide an undistortedimage or may have at least one surface of the transparent material notplane and/or not parallel with another surface, such as to give adistorted image effect. Perforated materials have perforation holeswhich allow light permeability.

Partially imaged light permeable panels are already known in severalfields and are typically used to control visibility of the panel,visibility of any image on one side of the panel, such as a graphicdesign, and visibility through the panel from one side to the otherside, and vice versa.

The incorporation of an opaque pattern on or into particular types oflight permeable panels, in order to create unidirectional vision, isalready known, for example in the construction of transparent walledsquash courts. These panels typically include a continuum opaque patternapplied in a single color, or with the pattern appearing one color fromone side of the panel but another color from the other side, to enhancethe one-way vision effect when one side of the panel is illuminated morethan the other side. A single color pattern is normally white or a lightcolor and a two color pattern is normally arranged to be white or lightcolor on the one side of the panel and black or dark color on the otherside of the panel, superimposed with exact or near exact registration,an arrangement which enhances the clarity of vision from the other sideto the one side. Such materials can be used to enable spectators ortelevision cameras to see through a squash court wall from the otherside while players on the one side can see the wall and cannot seeclearly through the wall to the other side. The pattern in such panelsis normally one of small dots such that, the eye of a spectator in theaudience who is at a distance from the panel cannot discern theindividual elements of the pattern, the elements being too small for theeye to resolve.

A simple unidirectional vision panel comprises an opaque pattern of dots1 mm diameter at 1.4 mm centers on a square grid appearing white fromone side and black from the other side, the other side being lessilluminated that the one side. Light incident on the white dots isreflected and scattered, which has the effect of obscuring visibilityfrom the one side into the other side. However, a substantially clearview is obtained from the other side through the panel into the oneside, albeit the intensity of light of the image is reduced by virtue ofthe degree of opacity, giving a “toned down” effect to the image, notdissimilar to tinted transparent panels. Such products are described inGB Patent No. 2118096.

Light permeable panels having an opaque “silhouette pattern” and adesign which is superimposed on or forms part of a “silhouette pattern”on one or both sides of the panel are also known, as described in GB.Patent No. 2165292 (sometimes referred to hereinafter as “the '292invention”). Such panels are used for a variety of purposes, such asadvertisements on the windows of retail windows, buses and taxis.Typically, a design of an advertisement is visible from outside thewindow while, from the inside, the design is not visible and an observerhas a substantially unobstructed view out. In GB Pat. No. 2165292, the“silhouette pattern” is defined to mean any arrangement of opaquematerial which sub-divides the panel into a plurality of opaque areasand/or a plurality of transparent or translucent areas.

For advertisements, the silhouette pattern covers a sufficientpercentage of the panel area, typically between 35% to 80%, and thedesign comprises sufficiently bright and varied colors, that the eye isattracted to the design and not the objects on the other side of thepanel, thus providing an impactful advertisement from outside. Thesilhouette pattern on the inside is typically colored black, whichprovides a tinted view from the inside to the outside.

However, it is a feature of the invention of GB Pat. No. 2165292 that“the design becomes decreasingly perceptible from the side of the panelfrom which the design is normally visible as the level of illuminationfrom the other side increases”, which may be referred to as the“decreasingly perceptible” feature.

FIG. 32 of GB Pat. No. 2165292 discloses 36 distinct vision controloptions enabled by the '292 invention. Columns 5 and 6 of FIG. 32illustrate another feature of the '292 invention, that “the designand/or silhouette pattern is substantially imperceptible from the sideof the panel from which said design and/or silhouette pattern isnormally visible when the level of illumination transmitted through thepanel from the other side of the panel substantially exceeds the lightreflected from the said one side of the panel”. This feature may bereferred to as the “substantially imperceptible” feature.

A further feature of panels according to GB Pat. No. 2165292 is that “aprincipal perceived image when viewing a panel changes from the designto a space on the other side when the illumination is altered fromrelative light on the one side and relative dark on the other side torelative light on the other side and relative dark on the one side.” Theprincipal perceived image in the space on the other side is intended toinclude sources of illumination or objects or surfaces in the space onthe other side. This feature may be referred to as the “principleperceived image” feature.

These features, of the design becoming less perceptible and eventuallybecoming imperceptible, as the level of illumination on the other sideof the panel is raised increasingly higher relative to the level ofillumination on the side from which the design is being observed, havebeen a problem to the exploitation of the '292 invention in certainsituations. For example, if an advertisement of the '292 invention isplaced on a retail window, the design will typically be visible in thehours of daylight. However, if there is not relatively high artificialillumination outside the retail premises during the hours of darkness,or the level of internal illumination of the retail premises isparticularly high during the hours of daylight, such advertisements maybe substantially imperceptible or not have sufficient visual impact forcommercial purposes, the principal perceived image being the inside ofthe retail premises and not the design. It is typically desirable insuch applications to have optional vision of the advertisement and theview inside, for security reasons. The brain can concentrate on thedesign or the view through the panel, as required. In some parts of theworld, where night-time robberies are relatively commonplace, it can beregarded as an advantage for the principal perceived image to changefrom the design on the advertisement in the hours of daylight, to theinterior space in the hours of darkness. However, in situations wherethe advertiser wishes to have an easily seen advertisement at all times,under all pertaining lighting conditions, the feature of the designbeing decreasingly perceptible with increasing relative illumination onthe other side is a significant problem and limits the exploitation ofthe '292 invention.

Also well known are “backlit” signs, which typically consist of atransparent and/or translucent design on a front panel and an enclosedsign box. A typical sign box contains an internal illumination device ofone or more sources of illumination, typically an array of fluorescentlight tubes, which illuminate the front panel from behind. Other“slimline” backlit signs typically rely on the edge illumination of atransparent material, such as an acrylic sheet, which incorporate anarray of prismatic surfaces or etched lines of varying thickness or iswedge shaped or otherwise provides a relatively uniform emission oflight throughout one surface of the edge lit panel. The design on thefront panel is normally visible in ambient lighting conditions but theperceived image of the design is substantially intensified when theillumination device is switched on, illuminating the sign from behind.Front panels typically comprise a photographic transparency or areprinted. It has been found that backlit sign front panels can beadvantageously produced by printing a design on one side of atranslucent white plastic material and the “verso” or mirror image ofthe design is printed on the other side of the translucent whitematerial, the two design impressions being substantially aligned or ‘inregister’. This arrangement produces a reinforced color effect and, withfour colour printing of a photographic image, a more realistic perceivedimage when illuminated. Also known are alternating backlit signs whichcomprise a transparent mask film with a regular pattern of opaque lineslocated in front of a backlit sign front panel transparency. The frontpanel transparency typically comprises alternating bands of a first anda second different image, the band widths being the same width as theopaque lines and forming a continuous composite transparency. The maskfilm is caused to move so that the opaque lines alternately mask thefirst or second images, thus providing an alternating sign. Also knownis an alternating sign achieved by locating a panel of the '292invention in front of a backlit sign. When the sign illumination isswitched off or down to a very low luminous intensity, the design on thepanel of the '292 invention is visible. When the sign illumination isswitched on or increased to a sufficiently high luminous intensity, thedesign on the front panel of the backlit sign becomes the principalperceived image.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided apanel comprising a sheet of light permeable material and a transparentor translucent design superimposed on or forming part of a base pattern(as herein defined), said design being visible from one side of thepanel and a mirror image of said design being visible from the otherside of the panel when a sufficiently high level of illumination isprovided on either side or both sides of the panel.

According to another aspect of the invention there is provided a panelcomprising a sheet of optically clear transparent material and atranslucent design (as herein defined) superimposed on or forming partof a base pattern (as herein defined), said design being visible fromone side of the panel and a mirror image of said design being visiblefrom the other side of the panel when a sufficiently high level ofillumination is provided on said one and/or said other side of thepanel.

According to another aspect of the invention there is provided a sheetof optically clear transparent material and a translucent design (asherein defined) superimposed on a base pattern (as herein defined), saidbase pattern comprising a layer of translucent material, said designbeing visible from one side of the panel and a mirror image of saiddesign being visible from the other side of the panel when asufficiently high level of illumination is provided on said one and/orsaid other side of the panel.

According to another aspect of the invention there is provided a sheetof optically clear transparent material and a translucent design (asherein defined) superimposed on one side of a base pattern (as hereindefined), said base pattern comprising a layer of translucent material,and a mirror image of said design is superimposed on the other side ofsaid base pattern.

A number of different vision effects are obtainable from the aboveaspects of the invention and different lighting conditions. A design canbe visible from one side of a panel and not visible from the other side.A mirror image of the design can be visible from the other side of thepanel but not from the one side. Clarity of vision can be maintainedfrom the one side to the other side with or without the exception of thearea covered by the design with clarity of vision through the other sideof the panel with or without the exception of the area covered by thedesign. Visibility from the one side to the other side can be totally orpartially obstructed throughout the area of the panel while there isclear or partially obstructed vision through the whole of the panel fromthe other side to the one side. Clear or partially obstructed vision isobtainable through the whole of the panel from the one side to the otherside while visibility throughout the whole of the panel from the otherside to the one side is totally or partially obstructed. Vision fromeither side can be totally or partially obstructed throughout the areaof the panel.

In all cases through vision can be obtained in either direction throughthe panel when the level of illumination perceived through the panelfrom the far side of the panel sufficiently exceeds the illuminationreflected from and/or transmitted through the base pattern and anydesign when observed from the near side of the panel.

The panels of the invention can be illuminated and/or the or each designarranged thereon such that the eye will tend to concentrate upon thedesign on the panel or look through the panel and concentrate on anobject or objects beyond the panel. When viewed from the other side ofthe panel an observer can concentrate upon the mirror image of thedesign visible on said one side or look through the panel andconcentrate on an object or objects beyond the panel.

In addition, it is a principal feature of the invention that anyillumination on or of the far side of the panel will illuminate thedesign visible from the near side of the panel, owing to the transparentor translucent nature of the design and base pattern. Dependingprimarily on the proportion of the area of the panel covered by the basepattern, the design colors and the coefficients of light transmissivityof the design and base pattern and ambient lighting conditions, anincrease in the level of illumination on the far side of the panel mayincrease or decrease the perceptibility of the design in relation to theperceptibility of any object or objects illuminated on the far side ofthe panel.

In all cases, it is a feature that ‘spotlighting’ (as defined herein)the far side of a panel of the invention will tend to increase theperceptibility of a design facing the near side of the panel, if theother conditions of illumination to either side of the panel areunchanged. It is possible to arrange the panel construction andconditions of illumination of a panel such that when a design on thepanel is normally observed from one side, that the principal perceivedimage changes from an object spaced from the other side of a panel tothe design on the panel by sufficient ‘spotlighting’ directed onto theother side of the panel without changing any of the other conditions ofillumination.

The design on one or both sides may be decorative and/or informative orfor other purposes. The panel of the invention may also allow for thecontrol of solar heat gain, glare or UV radiation received within forexample, a building, vehicle or other enclosure or shelter withoutunduly affecting the visibility outwards.

The invention allows the natural or artificial illumination of space toeither side from the other side, so that, for example, a panel of theinvention forming an advertisement can be placed in a window of abuilding and still allow daylight to enter the window, albeit of reducedintensity, coupled with vision out of the building.

The design on the panel is superimposed on or forms part of a pattern oftransparent or translucent elements which is referred to herein as a“base pattern”. The term “base pattern” as used herein is intended tomean any arrangement of transparent or translucent material which isdifferently colored to the “neutral background” of the panel.

The term “neutral background” as used herein is intended to mean thecolor or colorless nature of any transparent or translucent sheets ofmaterial within the panel or the areas of holes within a perforatedmaterial comprising a light permeable material within the panel.

The term “optically clear transparent material” as used herein isintended to mean a transparent material that has two substantiallyparallel and plane surfaces or otherwise allows clarity of vision fromone side of the material through the material, enabling the eye to focuson an object spaced from the other side of the material and thusproviding a substantially undistorted image of the object. The materialdoes not have to be colorless or “water clear” but may be tinted.

The term “translucent material” as used herein is intended to mean amaterial which will allow light transmission but is not an opticallyclear transparent material (as defined herein).

The term “translucent design” as used herein is intended to mean adesign comprising a translucent material (as defined herein). The designtypically comprises translucent inks, toners or other marking materials.Another part of a translucent design may be opaque. Another part of atranslucent design may comprise optically clear transparent material.

The “base pattern” subdivides the panel into a plurality of transparentor translucent base pattern areas and/or a plurality of neutralbackground areas. The base pattern may be in many forms, for example itmay be a regular geometric element in a regular layout, such as apattern of dots, a regular geometric element in an irregular layout, afree form element in a regular layout, a free form element in anirregular layout or a combination of regular and free-form elements inregular and/or irregular layouts. Instead of a number of separateelements with an interconnected neutral background zone, the basepattern can be a pattern of separate base pattern elements and separateneutral background areas, such as a pattern of lines. The base patternmay be formed by interconnected base pattern elements with separateneutral background areas, such as a net, grid or mesh pattern. The basepattern can, if desired, be a combination of interconnected base patternelements and separate base pattern elements.

All of such base patterns may be repeated over a unitary panel toproduce large areas or a large panel can be made up from smaller panels,for example in the manner of tiles.

The elements forming the base pattern are normally small such as dotspreferably of equal size on a regular grid, sometimes referred to in theprinting industry as a “half-tone”, or a pattern of lines, or a gridpattern comprising marking material or perforated material. The basepattern is typically a continuum and provides an even shading of tintingeffect in the absence of a design.

The term “design” as used herein is intended to mean any graphic imagesuch as indicia, a photographic image or a multi-color image of anytype. The design is typically perceived to be visually independent ofthe elements of the base pattern. This feature can be tested by anobserver adjacent to one side of the panel from which the design isnormally visible, who moves away from the one side of the panel in aperpendicular direction from the panel until any individual element ofthe base pattern can no longer be resolved by the eye of the observer,the design remaining clearly perceptible.

A cross-section taken through a panel of the invention typicallycomprises two outer edges of a sheet of optically clear transparentmaterial and alternate transparent portions and translucent portions ofsaid base pattern, at least one of said translucent portions comprisinga part of said design.

In order for the perceptibility of the design to dominate perceptibilityof elements of the base pattern or the transparent areas, it isrecommended that a panel be constructed such that a cross-section can betaken through any point within the area of a panel such that the averagewidth of the translucent portions is less than 6 mm and the averagewidth of the transparent portions is less than 3 mm. If a panel of theinvention is intended to be principally observed from a distance of lessthan 1 m, it is recommended that the average width of the translucentportions and the average width of the transparent portions both be lessthan 2 mm.

This invention has some similar characteristics to that of GB Pat No2165292, in that there is a sheet of light permeable material, and apercentage of the light permeable material is not imaged, typically toallow the desired degree of through vision or light transmission ineither direction, and the panel is partially provided with a pattern anda design is superimposed on or forms part of the pattern. However,instead of being opaque, the base pattern and design are lightpermeable, of either translucent or transparent colors that allow lightto pass through the base pattern, as well as to pass through theportions of the light permeable sheet that are not imaged. There are anumber of advantages of the present invention compared to the prior art.

According to one aspect of the present invention, any illumination ofthe far side of the panel will illuminate the transparent or translucentdesign image as seen from the near side of the panel, in a similarmanner to a “backlit” sign. Thus while any increase in illumination onthe far side of the panel will tend to increase the visibility ofobjects on the far side of the panel, this effect will be compensated tosome degree by an increase in the illumination of the design by virtueof the rear illumination passing through the translucent material andthus intensifying the design image. In this manner, providing sources oflight or very highly illuminated surfaces are not placed directly behinda panel, the design typically remains visible, even in conditions ofreasonably high illumination on the far side of the panel. The inventionthus overcomes the previously outlined problem of the prior art of the'292 invention, in which the design becomes less perceptible orimperceptible under such conditions of increased illumination on the farside. There are many other benefits of the invention.

The invention is radically different from existing backlit signs, inthat it allows visibility through the panel in either direction. Thisfeature, for example, enables panels of the invention to be applied toexisting windows without preventing vision out or in, as would be thecase with a conventional front panel of a backlit sign. Another criticaldifference between the present invention and the front panel of abacklit sign is that when the luminous intensity of light sourcesdirectly behind a backlit sign is increased the design on the frontpanel becomes correspondingly more perceptible. However, a similarincrease in the luminous intensity of light sources directly behind apanel of the present invention will typically not cause the design to bemore perceptible and typically will cause it to be less perceptible thegreater the increase in luminous intensity, as the perceptibility of thelight sources directly behind the panel will dominate over theperceptibility of the design. In order to effectively increase theperceptibility of a design on one side of a panel of the presentinvention, compared to the “through image” of the other side of thepanel, by means of increased illumination on the other side, it istypically necessary to locate the source of illumination outside theline of sight of the observer. For example, if a panel of the inventionlocated in a window of a building, a spotlight on the ceiling of a roomin the building will be directed so that its light is concentrated onthe other side of the panel. The spotlight source of light should not bevisible to an observer outside, or at least it should not be within hisline of sight of any part of the panel. Any increase in such directspotlighting of the other side of the panel will increase theperceptibility of the design and decrease the perceptibility of theimage on the other side of the panel, being the interior space of thebuilding behind the window, assuming other illumination conditionsremain the same. Such spotlighting would provide no increase in theperceptibility of the design of a panel of the '292 invention and wouldtypically reduce the perceptibility of the design by virtue of thespotlighting being partially reflected off the window to increase theillumination of the interior space.

Thus the invention has advantageous features which are different fromand indeed opposite to those of the prior art of both the '292 inventionand existing backlit signs.

A panel of the invention comprises a sheet of transparent or translucentimperforate material or a perforated material. A transparent ortranslucent material can be a rigid sheet or a flexible film and can be“water clear” or stained or otherwise tinted. For example, the inventionmay comprise paper or transparent or translucent plastics film, eithercalendered, extruded, cast or blown, such as polyvinylchloride film orpolyethylene film or polypropylene film or polyester film. Transparentor translucent rigid sheet materials which may form the sheet of lightpermeable material include glass, acrylic, polycarbonate or polyvinylchloride sheets. Transparent materials may be optically clear to seethrough such as a typical pane of window glass or sheet of acrylic withtwo, parallel, plane surfaces that allow an observer on one side of apanel to focus sharply on an object spaced from the other side of thepanel. Alternatively, such materials may be ‘deformé’ (not plane) orotherwise treated on one or both surfaces to give a distorted image ofany objects seen through the material. Translucent materials to whichthe invention may be applied include the above materials, but are dyed,pigmented or otherwise caused to be translucent, allowing light to passthrough the material but preventing an observer focusing upon any objectspaced on the other side of a panel when vision is attempted through thematerial. Perforated materials which may form the sheet of lightpermeable material include any of the above materials.

The base pattern and any design are typically applied to a sheet oflight permeable material using marking material, such as printing inks,dyes or electrostatic printing powder or liquid toners, but may comprisetinted film or other materials. A perforated translucent material may beused to form the base pattern onto which the design is superimposed or aperforated transparent material may be used to define the base pattern.The base pattern and design may be applied by any imaging process, suchas airbrushing, any digital printing system such as ink jet printing,screen printing, offset litho printing and gravure printing. The designand/or base pattern may be applied by transfer from a carrying surfaceor membrane, such as electronic imaging by such processes as 3MScotchprint (Trade Marks of 3M) or ceramic ink transfer, the ceramic inkto be typically fused into toughened glass.

The inks or other marking materials or other materials forming the basepattern and design should be transparent or translucent, such astraditional offset litho printing inks or the inks, dyes or toners usedin digital printing, which are also typically light permeable. Designsmay comprise multi-color printing systems such as two colour or fourcolor process systems, typically on an additional color background,typically white.

In one embodiment of the invention, the base pattern comprisestranslucent white ink to form a white translucent base pattern layeronto one side of a sheet of transparent material, such as water clear,transparent polyester film. The design is printed superimposed onto thewhite base pattern layer using transparent or translucent inks, by anyof the methods disclosed above or in GB Pat. No. 2165292 or in patentapplications PCT/GB96/00002 or PCT/GB96/02600 or any other methods toachieve close or substantially exact registration of the design inrelation to the base pattern. In all panels of the invention, it isimportant to consider and provide a suitable average lighttransmissivity of the design and base pattern, to achieve the desiredoptical performance. The design may be masked by the white ink and besubstantially invisible from the other side of the panel, particularlyif the design inks are maintained within the area of the base patternlayer and there is no or a low level of illumination on the one side ofthe panel. However, the design is visible from the said one side of thepanel and a mirror image of this design is visible from the other sideof the panel when a sufficiently high level of illumination is directedonto the said one side of the panel. When viewed from either side, anyobjects spaced from the far side of the panel will normally beoptionally visible, for example with substantially the same conditionsof illumination of the panel and the space on both sides. The eye cansee the design on the panel, or see through the panel, as the brainselects. In this example, the design is printed ‘recto’, a term usedherein as used conventionally in the printing industry, for a designprinted on a surface facing the direction of the one side of the panelfrom which it is primarily intended to be seen, sometimes termed theobverse side. If the design is printed onto a surface on the other sideof the panel but facing towards the one side of the panel, the design issaid to be printed ‘verso’, that is to say a mirror image of the designis printed, which will appear as the mirror image of the design from thesaid other, reverse side of the panel and will be seen as the design ifseen from the said one side of the panel.

In another embodiment of the invention, the other side of a transparentor translucent material is imaged with the base pattern using whitetranslucent ink and the ‘verso’ or mirror image of the design is appliedto the other side of the white translucent base pattern layer. Themirror image of the design will be visible from the said other side ofthe panel. The design will not be visible or not as visible from thesaid one side of the panel. However, when the level of illumination ofthe said other side of the panel is sufficiently high, the design willbe visible from the said one side through the translucent white baselayer. When viewed from either side, any objects on the opposite side ofthe panel will typically be visible, for example under substantially thesame conditions of illumination of the panel and the space on bothsides.

In a preferred embodiment of the invention, a transparent material suchas water clear, transparent polyester film is printed with a design‘recto’ onto one side of the film, to be followed by the base patternlayer of one or more layers of white translucent ink, to be followed bythe design again printed ‘recto’ onto the base pattern layer, using oneof the methods of achieving close or substantially exact registration ofthe successive layers of ink previously referred to. In this preferredembodiment, the design is normally clearly visible from the said oneside of the panel and the mirror image of the design is normally clearlyvisible from the said other side of the panel under the variety oflighting conditions encountered in a practical application of theinvention. The partial imaging of two ‘recto’ designe either side of atranslucent white ink base layer, according to this preferred embodimentof the invention, provides a number of advantages, in that the design orthe mirror image of the design is readily visible from the respectivesides of the panel and optional visibility of any objects on theopposite side of the panel is typically maintained.

In another embodiment of the invention, a similar effect can be achievedby printing a ‘verse’ design image on the other side of the transparentfilm, then applying a white translucent ink base pattern layer and thenprinting a ‘verse’ design on the other side of the white translucentbase pattern layer. Such a panel provides the additional benefit oftypically being applied inside a building or vehicle window, protectedfrom the outside weather, but the design being visible from the outside.

In another embodiment of the invention, the light permeable material isa preforated material, such as performed paper or perforated white orclear polyvinylchloride film, polyethylene film, polyester film orpolypropylene film, the perforated holes allowing vision through thepanel. The paper or film material which has not been removed inperforation defines the base pattern. This perforated material is imagedwith transparent or translucent marking materials, as required, toprovide the required design and base pattern colours and the requiredlight transmissivity of the base pattern and/or design and/or mirrorimage of the design. For example, one side of a water-clear perforatedplastic film is printed with a design ‘recto’, then one or more layersof white translucent ink forming a translucent base pattern layer areapplied throughout the base pattern, followed by the design printed‘recto’ once again. The design is visible from the said one side of thepanel and the mirror image of the design is visible from the other sideof the panel. The percentage of holes in the preforated film typicallyvaries from 55 per cent to 10 per cent of holes (45 per cent to 90 percent base pattern), depending on the optical performance characteristicsrequired of the design impact and vision through the panel, in eachdirection, bearing in mind the lighting conditions to which the panelwill be subjected in use. For a high visibility of design, a highpercentage of base pattern should be provided and/or a high level ofilluminance at the design surface on the panel.

In another embodiment of the invention, utilising transparentunperforated or perforated materials, the base pattern does not comprisea separate layer but the translucent design is printed photographicallyor otherwise imaged, for example by four or five color process printing,so as to appear similar to a photographic transparency but with theneutral background area or areas unimaged.

In the previously described embodiments, the paper or plastic film wayadvantageously be applied to a window by self-adhesive, typically awater-clear acrylic pressure-sensitive adhesive, the adhesive beingtemporarily protected by a siliconised filmic or paper liner on theopposite side of the self-adhesive to the film. The liner is removedbefore attaching the film to the window by means of the adhesive.

A translucent base layer covering a design can prevent visibility of thedesign form one side under certain lighting conditions, typicallyrelatively high illumination of the base layer compared to the designfrom the other side of the base layer. However, when sufficientillumination is provided on the other side of the panel, the design willbe visible through the translucent base layer. This feature can be usedto create an alternating sign, the design being alternately invisibleand visible as a light source directed from behind and onto the panel isswitched on and off. When the light sources is switched off, objects inthe space on the other side are typically visible. Thus for example, apanel on the window of a shop can provide alternating vision of thedesign on the panel and the interior of the shop.

The design image perceived and its intensity, and the visibility througha panel of the invention, depend upon a number of factors including thelighting conditions on either side of the panel, the lighttransmissivity and surface reflectivity of the transparent ortranslucent materials, the reflective refraction characteristics and thecontrast of the colors used in the design and/or base pattern, thedistinctiveness of the design, the ratio of base pattern area to neutralbackground area and the shape of the base pattern. Visibility of thedesign results from light incident from the observer's side of thedesign being reflected and scattered from the ink or other markingmaterial forming the design, or light incident on the other side of thepanel which is refracted through and scatters from the ink or othermarking material from the design and the base pattern.

Conditions, can be such as to allow the eye to see the design or to seethrough the design beyond an imaged transparent material, dependinginter alia upon the focus of attention of the viewing person, and uponthe proximity of the viewing person to the panel, as well as the otherfactors listed above as affecting the perception of a design image.

The design perceived from one side and the mirror image of the designperceived from the other side can be enhanced by spotlight illuminationof the panel from either or both sides, preferably directed to avoidillumination through the panel of objects that are visible through thepanel from a normal viewing position of the panel. Such Spotlighting isnormally directed downwards, for example onto a panel on a window froman external canopy or internal ceiling position. As another example, apanel on an internal glass partition is illuminated by spotlightingdirected downwards from the ceiling on one or both sides of the panel.Because of the refraction, reflection and scattering of rays from suchlighting which is incident upon a design of marking material, the effectis to enhance any design image seen by an observer. The observer doesnot have to be aligned with such spotlighting to gain the benefit of anenhanced image. A proportion of the light from such spotlighting passesdirectly through the neutral background transparent parts of the panelonto an area of the floor on the opposite side of the panel, that is notin the direct line of sight of an observer through the panel. In thisway, the visibility of a design can be greatly enhanced by concentratedrear illumination, while maintaining the desired degree of visibilitythrough the panel in either direction, which is not possible with, andrepresents a major advantage over, the prior art using an opaque patternor panels with a continuous transparent or translucent design providingno vision through the panel.

The terms ‘spotlights’ or ‘spotlighting’, as used herein, are intendedto mean any system of artificial illumination which is focused, directedor otherwise concentrated onto a panel or the invention. Typically, alight source such as a general light source bulb (GLS), a tungstenhalogen lamp, a metal halide lamp or a fluorescent or compactfluorescent tube may be silvered or otherwise made reflective over partof their surface or they may be combined with an optical reflectorsystem and/or an optical prism system and/or a shading system to enablea targeting the required area of illumination, in this case a panel ofthe invention, and to prevent or limit incident light on other surfaces.Thus the term “spotlighting”, as used herein, is not limited to anarrowly focussed beam of say 10′ angle of distribution but includes‘flood’ beams of say 25′ angle, “wide flood” beams of say 40′ angle andeven “very wide flood” beams of say 60′ angle, if they are located at adistance such that the beam is concentrated on (approximately subtendedby) the panel of the invention. One example is a spotlight fixed to aceiling which is directed onto the panel but not a substantial areaoutside the panel perimeter. Other examples of ‘spotlights’ include thetype of luminaires known as ‘picture lights’, ‘blackboard lights’ and‘billboard lights’, which are designed to provide a relatively uniformillumination of a panel, typically a rectangular vertical panel, theluminaire typically being in a position outside the space defined byperpendicular projection from the perimeter of the panel. Suchluminaires are normally used to illuminate the front or obverse side ofa opaque panel such as a picture or billboard without illuminating othersurfaces or obstructing vision of the panel. The same type of luminairescan advantageously be used to illuminate the panels of the presentinvention with a design feeling one side by their light being directedor concentrated on the other side of the panel. This desirable featureof illumination by a rear ‘spotlight’ may be arranged even moreadvantageously by ensuring that the observer's eye is outside the beamor space that is illuminated by the ‘spotlight’. It is additionallyadvantageous to shield the observer's eye from the actual light source,even if directed away from the observer's eye, as sources ofillumination appear bright and any such brightness in the field ofvision of the observer will tend to detract from the perceptibility ofthe design. It is often not realised that not only do designs on panelsof the '292 invention become decreasingly perceptible with an increasein the level of illumination behind a panel but that designs on anopaque substrate such as solid paper or plastic film will becomedecreasingly perceptible and may become completely imperceptible ifthere is a surrounding brightly illuminated area. For example, thedesign on a conventional opaque poster on a shop window will typicallybe invisible or not clearly visible during the hours of darkness unlessthere is good front illumination of the poster. The pupil of theobserver's eye adjusts to the general light level within the field ofvision, such as a brightly illuminated shop interior, and can then notdiscern the design on the opaque poster.

In contrast, suitable spotlighting of a panel of the invention frominside the chop will enable the design to be clearly visible under theotherwise same lighting conditions. Ideally such spotlighting should bearranged so that the normally intended opportunities for viewing thedesign will result in the observer's eye being outside the space definedby a geometrical projection of the panel by the light source, which maybe termed the “projected panel volume” on the observer's side of thepanel, as illustrated in FIG. 3. Thus the source of the spotlight willnot be in the direct line of eight from the observer's eye to any partof the panel. Also, the spotlighting which is incident upon anyoptically clear transparent area of the panel (typically forming theneutral background) will be directed towards the ground and notsignificantly detract from visibility of the design. Such spotlightingwould not benefit and indeed would tend to detract from the visibilityof the same design on opaque panels or panels of the '292 inventionbecause of internal reflection adding to the illumination of theinternal space.

Of course, spotlighting on the front, observer, recto side of a designwill also improve perceptibility of the design but this is often noteasy to arrange, for example illumination of a panel on a shop windowfrom outside is often not permitted by reasons of space ownership, leaseconditions or public planning or zoning restrictions. Thus the inventionhas unique advantages over the prior art in being capable ofillumination from inside a building to be visible from the outside, aswell as providing visibility through the panel.

The perceptibility by an observer of the design on one side of a paneland the perceptibility of the “through image” of the space and any lightsources, objects, walls or other surfaces in the space on the other sideof the panel may be assessed more precisely as follows.

The ratio of the base pattern area to the transparent area can beestablished for any base pattern. For example, consider a panel in whichthe base pattern is a regular pattern of straight lines of equal widthand equal spacing between lines. The ratio of the width of thetranslucent base pattern lines to the width of the transparent spacesbetween the base pattern lines represents the ratio of the base patternarea to the transparent area.

Typical ratio would be base pattern transparent area of 1:1 to 4:1. Thegreater the proportion of base pattern compared to the transparent area,the greater the perceptibility of the design compared to the “throughimage” of what is on the other side, and vice versa. The greater theluminance (cd/m²) of the base pattern compared to the luminance of thetransparent area, from the observer's side of the panel, the greater theperceptibility of the design compared to the “through image” and viceversa. Experimental tests undertaken to compare the performance of apanel of the invention with a panel of the '292 invention using anidentical geometrical pattern for the base pattern and silhouettepattern respectively (covering 80% of the panel area), on identicalsheets of optically clear transparent material and with an identicalrange of 32 different lighting conditions, measured by means of aluminance meter and human perceptibility appraised by a number ofobservers, show that roar illumination of a panel of the invention byone or two spotlights outside the direct line of sight of the observerprovides a dramatic improvement to the perceptibility of a panel of theinvention, whereas it has no perceptible effect on a panel of the '292invention. Depending upon the ambient lighting conditions, the luminanceof the panel is increased to up to seven times the luminance of a panelof the '292 invention under identical conditions, the minimum recordedbenefit in luminance being approximately twice that of the panel of the'292 invention. The human perceptibility of a panel of the inventionimproves by as such as from “surface not visible” (0 on a perceptibilityscale of 0 to 4) to “surface visible, detail very discernible” (4 on aperceptibility scale of 0 to 4).

In addition to the previously mentioned factors, the improvement inperceptibility of the design by spotlighting the other side of a panelis dependent upon the luminous intensity of the spotlights and theirdistance from the panel and the light transmissivity of the design andbase pattern, which will typically vary over the area of the design,typically being highest in areas of white or other light colour anddarkest in areas of black or other dark colour. It is found to betypically preferable to arrange the panel such that the average lighttransmissivity of the panel over the area of the design and base patternis greater than 3.0% of incident light on the panel and that areas ofwhite have a light transmissivity of preferably greater than 5.0%.However, panels with an average light transmissivity of the design andbase pattern of as low as 1% can offer functional advantages compared topanels according to the prior art. For most panels, for example panelsused for window advertisements, it is found to be preferable to have arelatively high proportions of base pattern such as 1.6 mm wide lines at2 mm centers, which provides a base pattern:transparent area ratio of4:1.

The visibility of perceptibility of a design compared to the “throughimage” will always be increased by suitable “spotlighting” as describedabove, directed onto the far side of a panel of the present invention.The effect of increasing the general (illumination of the space and anyobjects, walls or other surfaces in the space on the other side can beassessed by first establishing the ratio of base pattern to transparentarea and the light transmissivity of the design and base pattern andthat of the transparent area. It is then possible to calculate the ratioof light transmission through the design and base pattern compared tothe light transmission through the transparent area, which can beconsidered to represent the luminance of the design and basepattern:luminance of the transparent area (which in turn provides a goodapproximation of the visibility of the design:visibility of the “throughimage). For example, if a panel with a base pattern:transparent arearatio of 4:1 has a transparent material light transmissivity of 90% andan average transmissivity of 5% through the design, base pattern andtransparent material, then the resulting light transmission ratioresulting from general illumination of the space behind would be:${\frac{4 \times 5}{100} \cdot \frac{1 \times 90}{100}} = {2:9}$

meaning that increasing the general illumination behind the panel woulddecreases perceptibility of the design. However, if the combinedtransmissivity of the design and base pattern and transparent materialwas 30%, the ratio would be${\frac{4 \times 30}{100} \cdot \frac{1 \times 90}{100}} = {4:3}$

meaning that increasing the general illumination behind the panel wouldincrease perceptibility of the design. Typically, spotlight illuminationdirected onto the front or rear of a panel is required to achievesubstantial improvement in design visibility compared to “through image”visibility.

The typical feature of the principal perceived image changing from the“through image” to the design on one side of a panel by spotlighting theother side of the panel may be tested as follows. An observer is locatedat a suitable distance, typically 1-2 m, on the one side of the panel.An object is placed at a suitable distance, typically 1-2 m, from theother side of the panel. Illumination on both sides of the panel istotally or substantially eliminated. Then the level of illumination isgradually raised on the other side of the panel only, either byspotlighting the object or general illumination encompassing the object.The illumination should only be raised to a level at which the object isreadily discernible, with or without any surrounding objects, such thatthe “through image” forms the observer's principal perceived image.Without changing other conditions of illumination, spotlightillumination is then directed onto the other side of the panel. Thespotlight illumination is raised to a level at which the principalperceived image changes from the “through image” to the design on thepanel.

In another embodiment, the light permeable material is a tinted lightpermeable material, such as a polyester film dyed a ‘neutral’ grey tint,which also will increase the one-way effect of a base pattern and designapplied to one side of a panel, typically partially or totally obscuringvision through the panel from the one side, while maintaining visibilityfrom the other side to the one side.

In another embodiment, a transparent or translucent base portion anddesign may be applied to a light permeable material comprising apartially metallised mirror material, such as is typically used as aone-way mirror or as ‘solar glazing’, to reflect a proportion of solarradiation to reduce heat gain, solar glare and UV degradation inside abuilding. Such products increase the one-way effect of either a panel ofthe invention in isolation or the partially metallised material inisolation, and enable hold advertisements or designs on one side of apanel while maintaining visibility through the panel from the oppositeside. The principal advantage of the invention, that a design can bemade more perceptible by illumination from either side or both sides ofa panel, still applies to embodiments incorporating partially metallisedmaterials.

In another embodiment, a partially or totally metallised mirror materialis placed at a distance behind a panel of the present invention. Whenviewed from the design side the mirror reflects the ‘verso’ image into a‘recto’ image, perceived to be twice the distance away from the panel asthe distance to the mirror surface, which leads to a variety ofinteracting visual effects, of practical value in promotional and otherfields. If the mirror is partially mirrored, vision is still enabledthrough the partial mirror and the panel of the invention, from theother side of the partial mirror. This has many useful applications, forexample, as a covert observation device disguised as a promotional sign.

Preferred methods of producing the design and base pattern include theuse or adaptations of those methods for producing a design andsilhouette pattern disclosed in GB Patent No. 2165292. Some of thesemethods utilise differential adhesion of different ink layers to achievesubstantially exact registration, as disclosed in FIGS. 20 and 21 of the'292 patent. Another preferred method utilises conventional printingmethods with a dimensional registration tolerance system to achieveconsistent visual images, described as the Overlap Method in GB PatentNo. 2165292. Improvements to such methods of partial imaging aredisclosed in patent application PCT/GB96/02600. A particular advantageof the present invention, in which opacity is not required, is thatoffset litho or digital printing systems, that typically use transparentor transiucent inks, can be used without the need to build up manylayers of ink to achieve opacity, as is required for the '292 invention.For example, with litho printing, as many as six layers of black andeight layers of white ink are required to achieve an opaque backgroundwhite layer to a design with an opaque black layer behind. For thepresent invention, one or two layers of white ink are adequate for mostembodiments, as a translucent background to a design. Thus the designand base pattern of the present invention may be produced in one pass ofa six color offset litho printing press as opposed to three or fourpasses required for a panel according to GB Patent No. 2165202. Thedesign and base pattern of the present invention may be produced by oneor two passes of a four or five color digital printing process, such asink jet printing. The present invention is typically much easier toprint by any litho or digital printing system compared to the '292invention,, as less layers and therefore less registration of layers isrequired. Instead of producing the base pattern and design bysuperimposing layers, they can be co-ordinated in one printing processby means of artwork which is restricted to areas related to elements ofthe base pattern, for example by means of four color can be produced inone impression, for example by transfer from a carrier layer, forexample by means of an electronic imaging system such as 3M Scotchprint(Trade Marks of 3M) or digital offset litho printing by such equipmentan Indigo (Trade Mark of Indigo NV). Raster Image Processing techniquescan be used to determine the required application of four or five colorprocess inks from a single piece of artwork, such as a conventionalphotographic image.

The base pattern need only cover part of a panel, the remainder beingleft without a base pattern. Alternatively, other parts of a panel ofthe invention may have an opaque “silhouette pattern” according to GBPatent No. 2165292, with a design on one side or a design on both sides,or have one or more relatively large opaque areas onto which indicia orother designs can be superimposed, such arrangements being ideal where amirror image of a design of indicia or other subject is not acceptableor not preferred. Thus an advertisement might have a pictorial sectionaccording to the present invention and a section with indicia forming apromotional message according to GB Patent No. 2165292 in another partof the same panel.

Additional benefit can be obtained if the base pattern can be arrangedto be geometrically the same as the opaque silhouette pattern and forthe two patterns to be geometrically continuous. Thus a design canappear to be of a consistent perceived quality under certain lightingconditions but a secondary or subliminal design can be incorporated thatwill only be clearly visible under other lighting conditions. Forexample, a panel could have a primary design of the name of a shop orproduct brand. A secondary design, for example the indicia “NIGHT SHOP”,could be formed of opaque elements within these indicia, surrounding thebase pattern of a continuous, similar geometry. If fixed to a shopwindow, only the primary design would be visible during the hours ofdaylight. However, during the hours of darkness, the primary designwould be substantially less visible and the secondary design “NIGHTSHOP” would be clearly visible as a silhouette. A related silhouetteeffect has been created using the '292 invention with a differentsilhouette pattern with a different percentage opacity for the secondaryimage, this secondary image being therefore clearly visible at alltimes. This secondary design feature of the present invention thusrepresents an improvement over the prior art.

An alternating sign can be achieved using a panel of the inventioncomprising a sheet of optically clear transparent material as a frontdesign panel in an assembly also incorporating a conventional opaquerear design panel. At least one intermediate light source is provided,preferably offset outside the space defined by the perimeters of the twopanels. When the rear design panel is not directly illuminated, thefront design panel of the invention is clearly visible owing to theambient illumination in front of the sign and/or spotlight illuminationof the front design panel by an offset intermediate light source. Whenonly the rear design panel is illuminated by an offset intermediatelight source, the rear design becomes the principal perceived image asthe luminance produced from the illuminated rear design is substantiallygreater than the luminance of the front design and base pattern. As analternative to a switching or dimming system to alternate directillumination of the two design panels by two offset intermediate lightsources, a rocking optical reflector system or prism system, typicallyactivated by a rotating cam, can alternate directed light from a singleoffset light source between the front design panel and the rear designpanel. The luminance of the front design panel of the invention can beenhanced by a “Light Redirecting material”.

The term “Light Redirecting Material” (LRM), as used herein, is intendedto mean one of a range of sheet or film materials with linear prismaticprojections or recesses, typically on one surface, or prismatic airvoids spaced within an otherwise solid sheet of plastic material, suchas acrylic or polycarbonate. One such material is 3M Scotch OpticalLighting Film (SOLF) manufactured by the Minnesota Mining andManufacturing Company, which has a linear triangular prismatic surface.Another LRM is SERRAGLAZE by de Montford of Lichfield, UK, whichincorporates ‘air shelves’ within a plastic sheet having plane externalsurfaces. Such materials redirect light incident on their surface withina specified range of angle of incidence, by means of internalreflection. Other terms commonly used for such materials include “lightmanagement materials” and “daylight improvement films”, as one purposefor such films is to redirect light incident on a building window to amore horizontal light path or to redirect the daylight upwards ontoceilings within the building, the ceilings typically being morereflective than the building floor and thus also increasing the“daylight factor” of the internal illumination of the building.

Existing LRM would typically be counter-productive when used with panelsof the present invention as the incident light redirected onto thedesign would also be redirected through the transparent areas and thuscause glare, detracting from visibility of the design. However, thisinvention includes new light redirecting materials which have beendeviced, and new ways of using some existing Light RedirectingMaterials, principally to enhance the visibility of the design withoutcorresponding glare.

Such newly devised materials or applications can be incorporated intopanels of the invention for other purposes, such as to enhance privacyglazing. Privacy glazing using panels of the '292 invention cuffers theproblem of becoming ineffective during the hours of darkness, as typicalinternal illumination enables an observer outside to see through panelsof the '292 invention, as previously described. The present inventionovercomes this problem, typically incorporating internal spotlightingonto the privacy windows, as part of the interior lighting system. Lightredirecting materials have been devised of adapted to enhance thevisibility of the design by redirecting daylight and/or spotlightingincident on the panels onto the design and not into the eye of theobserver. Optionally, daylight can be redirected partly onto theceiling, to compensate for the shading effect of the design and basepattern. Existing privacy glazing panels according to the '292 inventiontypically are manufactured to have a silhouette pattern of black dots orlines facing inside the room to assist vision out. A translucent basepattern layer of black or grey marking material may be incorporated intoembodiments of the present invention, typically with a superimposedwhite base pattern layer as a background on which to apply the designcolours.

Panels of the invention may be edge lit. Edge lighting of panelsaccording to GB Pat. No. 2165292 was disclosed in that document. Lightis internally reflected down a sheet of transparent material. That lightwhich is incident on the design applied to one surface of the panel isscattered and some of the scattered rays pass out of the other side ofthe panel, making the design visible to an observer. However, suchpanels have a disadvantage in that from the one side of the panel, anobserver typically sees an unwanted mirror image of the design which isreflected off the other panel surface. A design applied to the onesurface and facing a panel of the present invention is seen as a mirrorimage of the design from the one side of the panel. The reflection fromthe other surface, of a mirror image of the design, thus reinforces thevisual impact of such an edge lit sign. Thus, the present inventionprovides an improvement to edge lit signs.

GB Pat. No. 2165292 discloses the projection of designs onto an opaquesilhouette pattern, for example by a slide projector. An embodiment ofthe present invention of a projected design onto a translucent basepattern represents an improvement over the prior art, in that theprojected design is visible from one side of a panel and a mirror imageof the design is seen from the other side, as well as the panel allowingthrough vision. For example, a panel with a base pattern comprising awhite layer may be installed in a retail store window. This base patternwill typically allow visibility in and out of the shop during thedaylight or opening hours. When the shop is closed during the hours ofdarkness, images may be projected onto the panel in the store windowfrom inside the store, for example as a promotional display. This rangeof features is not possible with the prior art of the '292 invention orconventional back projection screens.

BRIEF DESCRIPTION OF THE DRAWINGS

Further specific embodiments will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 illustrates a variety of arrangements of light permeable materialand applied designs and base layers which may be advantageously adopteddepending on the functional requirements of a particular product.

FIG. 2 illustrates a number of vision control effects obtainable fromthe invention;

FIG. 3 illustrates optional arrangements for illustrating panels of theinvention;

FIG. 4 is a diagrammatic cross-section of a panel located in an opaquepartition wall;

FIG. 5 illustrates three panels with different base patterns anddesigns;

FIG. 6 illustrates opposite sides of another panel of the invention;

FIG. 7 illustrates two cross-sections through transparent sheetmaterials; and

FIG. 8 illustrates cross-sections through Light Redirecting Materialsand components thereof.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1/1-6/1 illustrate six embodiments with an imperforate transparentor translucent material 23 with a single design printed ‘recto’ 43 or asingle design printed ‘verso’ 63, some embodiments having a translucentbase layer 83, which for example comprises one or more layers of whiteink or one or more layers of white ink on a layer of black or grey ink.

FIGS. 1/1-1/2 illustrate seven embodiments with an imperforatetransparent or translucent material 23 with two design impressions,either printed ‘recto’ 43 or ‘verso’ 63 or one ‘recto’ 43 and one‘verso’ 63 and a translucent base layer 83. All of these thirteenembodiments can have equivalent arrangements but with a perforatedtransparent or translucent material.

FIGS. 1/1-1/3 illustrate just three such embodiments in which theperforated material 310 is imaged in similar arrangements of ‘recto’design 43, ‘verso’ design 63 and base layer 83 to the embodiments inFIGS. 1/1/1, 1/2/2 and 1/3/2 respectively.

FIGS. 1/4/3 illustrate a panel having a design over only part of atranslucent white base layer. FIGS. 1/5/3 and 1/6/3 illustrates panelshaving more than one base layer, for example base layer 123 could be atranslucent greytone which permits better vision through the panel thana translucent white base layer 83. There are many other possibleconfigurations.

FIG. 2 illustrates a number of vision control effects enabled by theinvention. In each diagram, 21 represents a panel of the invention, 41represents attempted vision through a panel 21, 81 being an objectvisible beyond the panel, otherwise through vision is obstructed andterminated by panel 21 or the dashed lines indicate alternative visionthat can be optionally concentrated upon the design 61 and/or the basepattern on the panel or can be concentrated on the object 81, at thewill of the viewer. 61 represents vision of a design on the left handside of the panel and 61′ represents vision of a mirror image of thedesign on the right hand side of the panel. The different vision controleffects are enabled by selection of base patterns, designs and lightingconditions applied to panels.

FIG. 3 illustrates optional arrangements for illuminating panels of theinvention.

FIG. 3A is a diagrammatic cross-section through the window 2 in abuilding with a panel of the invention 8 attached to the window 2 with adesign 16 facing outside the building towards an observer 4. Generalsources of internal illumination 10 illuminate the internal space insidethe window, including object 14 which is visible to the observer 4through the panel 8. An internal spotlight 12 can be directed onto theinside of the panel 8. Rays of light from the spotlight 12 incident uponthe transparent neutral background 26 of panel 8 are transmitted ontoprojected area 18 on the floor and do not cause glare in the eye 6 ofthe observer 4. Light incident on base pattern 22 is scattered andexample ray of light 20 from spotlight 12 is redirected through the basepattern 22 and design 16 towards the eye 6 of observer 4. The spotlight12 is outside the line of sight of eye 6 throughout the area of thepanel, the upper bound sightline 24 passing below the spotlight 12, withspotlight 12 not switched on, object 14 would typically be the principalperceived image of the observer 4 during the hours of darkness, withdesign 14 typically being only faintly visible. When spotlight 12 ofsufficient luminous intensity is turned on, the principal perceivedimage of observer 4 changes from object 14 to design 16. By alternatelyswitching the spotlight 12 on and off, the principal perceived imagealternates between the design 16 to object 14 within the interior space.In the hours of daylight, it will typically be possible to see out ofthe window 2 through the panel 8.

FIG. 3B is a diagrammatic partial perspective of FIG. 3A with window 2partially cut away. The geometrical projection of the panel 8 from thespotlight 12 includes the light from spotlight 12 which passes throughthe transparent neutral background of panel 8 and which is incident onthe floor over the area 18. The projected space between the panel 8 andthe floor area 18 is termed the “projected panel volume”. The eye 6 ofobserve 4 should be outside this projected panel volume for thespotlight 12 to effectively illuminate the design 16 on panel 8 in a waythat improves the visibility of design 16 to observer 4.Correspondingly, the spotlight 12 should not be within the perimeterpanel sightlines 24 of the eye 6 of observer 4 for the advantageousillumination of design 16 spotlight 12 without any resulting glare inthe eye 6 of observer 4.

FIG. 4 is a diagrammatic cross-section of a panel of the invention Rlocated in an opaque building partition 38. The panel 8 is constructedsuch that a design 16 is visible from one side (the left hand side) ofthe panel and its mirror image 16′ is visible from the other side (therighthand side) of the panel. Sources of general illumination 30 andspotlight 32 are located on the one side of the panel, together withobserver 4. Sources of general illumination 10 and spotlight 12 arelocated on the other side of the panel, together with observer 34.Observers 4 and 34 and panel 8 are aligned such that observer 4 alsoacts as an object 4 which may be visible by observer 34 and observer 34also acts as an object 34 which may be visible by observer 4, dependingon the conditions of illumination. All sources of illumination 10, 12,30 and 32 are dimmable.

In FIG. 4A, if there is no illumination to either side of the panel,neither observer can see the panel or each other. In general lighting 10alone is gradually raised in luminous intensity only to a level thatobject 34 just becomes clearly visible to observer 4, then design 16 istypically just faintly discernible also, but the principal perceivedimage comprises object 34. Spotlighting 12 can then be turned on andincreased in luminous intensity until design 16 becomes the principalperceived image of observer 4. If panel 8 has a particularly low averagetransmissivity of the design and base pattern, it may be necessary toreduce general lighting 10 in order for design 16 to become theprincipal perceived image of observer 4. In either case the principalperceived image changes from the “through image” to the design 16 onlyby means of changing the illumination on the other side of panel 8.Depending on the construction of panel 8, the mirror image of the design16′ may be visible to observer 34 with just the general lighting 10 orspotlight 12 or both means of illumination. However, if a base portionlayer masks the mirror image of the design 16′, for example asillustrated in FIG. 1/3/1, then the mirror image of the design 16′ canbe made clearly visible to observer 34 as shown in FIG. 4B. With theother sources of illumination turned off, spotlight 32 is raised inluminous intensity until the otherwise masked mirror image of design 16′is clearly visible to observer 34.

In FIG. 4C, general lighting 10 and 30 and spotlighting 12 and 32 can beadjusted so that the object 34 and design 16 are optionally visible toobserver 4, who can concentrate on either image, and object 4 and themirror image of the design 16′ are optionally visible to observer 34.

With no illumination on the one side of the panel and only spotlight 12illumination of the other side, good visibility of design 16 cantypically be achieved with an average luminance of panel 8 of from 10-30cd/m², as seen by observer 4. With levels of general illumination on theother side typical of building interiors, spotlighting 12 might beneeded to increases the average luminance of panel 8 from 30-70 cd/m²,as seen by observer 4, to achieve good visibility of design 16 with noillumination on the one side.

FIG. 5 illustrates three different panels 8 with different base patterns22 and different superimposed designs 16.

FIG. 5A illustrates a transparent film 2 of self-adhesive polyester filmwith a white, dot, translucent base pattern 22 and grey design 16 ofindicia, typically printed by one of the methods outlined in CB2165292or PCT/CB96/02600 to achieve substantially exact registration or closeregistration of design 16 superimposed on base pattern 22. The area ofneutral background around the dots 26 appears dark, as if there is noillumination behind panel 8. The panel of FIG. 5B is of similarconstruction, but comprises a dark line base pattern 22 and a whiteindicia design 16 which may be superimposed on the base pattern or mayalternatively comprise a white line base pattern revealed by the darksurround to the indicia.

FIG. 5C illustrates a panel of different construction, having a white,perforated material base pattern 22 typically comprising a whitepolyvinyl chloride self-adhesive film 2 perforated by mechanicalpunching. Alternatively base pattern 22 could be a perforatedtransparent film coated with translucent white ink before or afterperforation. Translucent design 16 of dark indicia is printed on thewhite base pattern, typically by screen printing or any method ofdigital printing. The circular hole perforation 26 are shown grey.

The self-adhesive materials above typically comprise a film layer, anadhesive layer and a liner which is removable in order to attach thefilm layer by means of the adhesive layer to a window or othertransparent sheet material.

FIG. 6 illustrates opposite sides of the same panel 8.

FIG. 6A illustrates one side of panel 8 with white indicia design 16superimposed on a dark, line base pattern 22 with a clear transparentneutral background 26 being part of transparent sheet 2.

FIG. 6B illustrates the other side of panel 8 with the mirror image ofthe design 16′ visible from the other side. FIG. 6B also illustrates theprinting of a “verso” design on the other side of a panel to be seen inits correct form from the one side of the panel, similar to FIG. 1/3/2.

FIG. 7 illustrates two diagrammatic cross-sections through transparentsheet materials.

FIG. 7A is a cross-section through part of a typical panel of the '292invention.

FIG. 7B is a cross-section through part of a typical panel of thepresent invention.

In FIG. 7A transparent sheet 40 is printed on one side with an opaquesilhouette pattern of dots or lines comprising a black layer 44 and awhite layer 46. A design 48 is superimposed on some of the opaqueportions. Layers 44, 46 and 48 are superimposed with substantially exactregistration such that design 48 is not visible from the other side ofsheet 40 to an observer 4. Light 54 from the one side, incident ondesign 48, is reflected and scattered, enabling observer 50 on the oneside to see the design 48. Light 56 from the other side is refractedthrough the transparent sheet 40 and is absorbed by the black layer 44,enabling substantially unobstructed vision through the transparentportions between the black silhouette pattern portions, providing goodvisibility of object 14 on the one side, the opaque silhouette patternportions being of sufficiently small width, typically of the order of 1mm, to be unresolvable by the eye from a certain distance. Depending onthe conditions of illumination, observer 50 can optionally see object 58on the other side or design 48. If there is no light 54 but light 56illuminates object 58, for example if observer 50 is outside a buildingduring the hours of darkness and sheet 40 is a window in the building,internal illumination 56 will typically cause object 58 to be theprincipal perceived image seen by observer 50.

FIG. 7B illustrates a panel of the present invention constructed in asimilar manner to FIG. 1/2/2. Transparent sheet 40 has two sides and twoouter edges. A cross-section through the panel comprises alternatetransparent portions and translucent portions of the base pattern. Thetranslucent portions comprise a printed, translucent, white base patternlayer 64 and a translucent design layer 68 is printed “recto” on thetransparent sheet 40 and a separate translucent design layer 68 isprinted also “recto” on the base pattern layer 64. The two design layers68 and the base pattern layer 64 are typically printed by one of themethods outlined in GB2165292 or PCT/GB96/02600 to achieve substantiallyexact registration or close registration of the three layers. Each ofthe three layers may comprise multiple layers or multiple applicationsof ink, for example the design 68 could be printed by a four colorprinting process. Part of the light 54 from the one side incident ontransparent portions 70 is refracted through the transparent sheet 40.Part of the light 54 from the one side incident on design 68 or basepattern 64 is reflected and scattered, enabling observer 50 on the oneside to see design 68. Another part of the light 54 incident on design68 or base pattern 64 is transmitted through the translucent portionsand is scattered and retracted through the transparent sheet 40 enablingobserver 52 on the other side of the panel 50 see a mirror image ofdesign 68 by virtue of light 54 from the one side. Similarly, observer50 can see design 68 by virtue of light 56 from the other side,transmitted through the translucent portions 62. For example, if sheet40 is the window of a building and sufficient internal illumination 56is concentrated on the inside of sheet 40 during the hours of darkness,then the principal perceived image seen by observer 50 outside thebuilding will be the design 68 and not internal object 58, the oppositeeffect to that resulting from similar conditions of illuminating a panelof the '292 invention as described for FIG. 7A. It can be seen thatvisibility of a design or visibility through a panel from either sidecan be controlled by the illumination on either side of the panel.

FIG. 8 illustrates cross-sections through Light Redirecting Materialsand their components.

FIG. 8A is a cross-section through SERRAGLAZE film 80 of de Montford,Lichfield, United Kingdom, manufactured by the Minnesota Manufacturingand Mining Company in two components 82 and 84 which are adheredtogether at surfaces 86 leaving air gaps 88. The air gaps 88 formdiscontinuities or “air shelves” which cause internal reflection oflight rays within a range of angles dependent upon material used,typically acrylic or polycarbonate. Light ray 91 is conventionallyrefracted downwards through the material whereas ray 93 is internallyreflected upwards. The material is intended to be used to improve thedaylighting through building windows by reflecting a proportion ofincident daylight upwards onto the ceilings of rooms, which aretypically light and reflective and “throw” the daylight further insidethe interior space.

FIG. 8B is a cross-section through a panel 100 of the present inventionsimilarly formed of two components 102 and 104 of combined width ofbetween 2 mm and 10 mm, typically of acrylic or polycarbonate. Thecomponents interlock and are adhered at surfaces 106 leaving air gaps108. Daylight rays incident on the panel and refracted into the panelare redirected. Light ray 101 is refracted down through the panel. Lightray 103 is reflected off the air gap 108 onto design 16 and base pattern22. Light ray 107 is incident on design 16 and base pattern 22. Lightray 105 is reflected off air gap 108 upwards. Thus such a lightredirecting panel increases the light incident on a design and basepattern and, therefore, their visibility. If used as a privacy glazingmaterial or a sign in a building window, the shading effect of the basepattern is partly compensated by the improvement to daylighting causedby reflecting rays towards a ceiling. Conversely, if the panel isconsidered to be reversed and rays 101, 103, 105 and 107 result frominternal spotlighting, the visibility of the design and the privacyachieved during the hours of darkness are improved.

FIG. 8C is a cross-section through component 102. It can be seen thatflat surfaces 110 of the castellated cross-section facilitate imagingwith a base pattern and design with exact registration by many printingprocesses, including screen printing and transfer processes in which anoverall continuous layer of ink or transferred material can be appliedto surface 110, but would not be able to image the recesses betweenthese protruding surfaces.

FIG. 8D is a cross-section through component 104. Many other embodimentsof the invention enhanced by light redirecting configuration arepossible.

What is claimed is:
 1. A panel comprising a sheet of colored orcolorless transparent material and a transparent or translucent design,said transparent or translucent design being superimposed with a basepattern which extends over the area of said sheet covered by said designand being adhered to at least one of said base pattern and said sheet ofcolored or colorless transparent material, said base pattern comprisinga translucent base layer and subdividing the panel into a plurality ofareas of said base layer and/or a plurality of areas of said colored orcolorless transparent material, said layers being constructed andarranged such that the whole of said design is visible from a firstviewing position located on one side of the panel when a sufficientlyhigh level of illumination is provided on the other side of the paneland a mirror of the whole of said design is visible from a secondviewing position located on the other side of the panel when asufficiently high level of illumination is provided on said one side ofthe panel.
 2. A panel as claimed in claim 1, wherein said base patternis extends over the entirely of said sheet.
 3. A panel as claimed inclaim 1, wherein said base pattern comprises a plurality of geometricelements arranged in a regular layout.
 4. A panel as claimed in claim 1,wherein said base pattern comprises an even continuum.
 5. A panel asclaimed in claim 1, wherein a cross-section of the panel comprises twoouter edges of said sheet of colored or colorless transparent materialand alternate translucent portions and transparent portions of saidpanel, and wherein the average width of said translucent portions isless than 6 mm and the average width of said transparent portions isless than 3 mm.
 6. A panel as claimed in claim 5, wherein the averagewidth of said translucent portions is less than 2 mm and the averagewidth of said transparent portions is less than 2 mm.
 7. A panel asclaimed claim 1, wherein the ratio of base pattern area: transparentarea is in the range of 1:1 to 4:1.
 8. A panel as claimed in claim 1,wherein said base layer comprises an ink.
 9. A panel as claimed in claim1, wherein said base layer is white.
 10. A panel as claimed in claim 1,wherein said base layer comprises a grey material.
 11. A panel asclaimed in claim 1, wherein said base pattern comprises a perforated,translucent material.
 12. A panel as claimed in claim 1, wherein saidsheet of transparent material is imperforate.
 13. A panel as claimed inclaim 1, wherein said sheet of transparent material is perforated.
 14. Apanel as claimed in claim 1, wherein said panel is configured such thatan observer on one side of the panel can see through the panel when thelevel of illumination perceived through the panel from the other side ofthe panel sufficiently exceeds the illumination reflected by said panelwhen observed from said one side of the panel, and an observer on saidother side of said panel can see through the panel when the level ofillumination perceived through the panel from said one side of the panelsufficiently exceeds the illumination reflected by said panel whenobserved from said other side of the panel.
 15. A panel as claimed inclaim 5 or claim 6, wherein said design comprises a design layer andwherein, within each of the translucent portions, said base layer hastwo outer edges and said design layer has two outer edges and the twoouter edges of said design layer are located within the two outer edgesof said base layer.
 16. A panel as claimed in claim 1, wherein a firstdesign layer is printed onto said sheet of colored or colorlesstransparent material, said base layer is printed onto said first designlayer, and a second design layer, substantially identical to said firstdesign layer, is printed onto said base layer.
 17. A panel as claimed inclaim 1, wherein the mirror image of said design is printed onto saidsheet of colored or colorless transparent material.
 18. A panel asclaimed in claim 1, wherein the mirror image of said design is printedonto said base layer.
 19. A panel as claimed in claim 1, wherein saiddesign and said base pattern have been formed by offset litho printing.20. A panel as claimed in claim 1, wherein said design and said patternhave been formed by a digital printing system.
 21. A panel as claimed inclaim 1, wherein said design and said base pattern have been formed byink jet printing.
 22. A panel as claimed in claim 1, wherein said designhas been applied by means of transfer from a carrying surface ormembrane.
 23. A panel as claimed in claim 1, wherein said design hasbeen applied by means of ceramic ink transfer.
 24. A panel as claimed inclaim 1, wherein said design has been printed by a four colour printprocess.
 25. A panel as claimed in claim 1, wherein said panel has alight redirecting surface disposed between front and rear surfacesthereof substantially at an angle to said front and rear surfaces, saidlight redirecting surface being configured and disposed so as toredirect incident light by reflection.
 26. A panel as claimed in claim25, wherein said light redirecting surface includes at least one surfaceformed as part of a prismatic projection of said sheet of colored orcolorless transparent material.
 27. A panel as claimed in claim 25,wherein said light redirecting surface includes at least one surfaceformed as part of a prismatic recess of said sheet of colored orcolorless transparent material.
 28. A panel as claimed in claim 25,wherein said panel has a void formed therein and said light redirectingsurface constitutes a boundary of said void.
 29. A panel as claimed inclaim 25, wherein said design and said base layer are disposed betweensaid front and rear surfaces of said panel.
 30. A panel as claimed inclaim 1, wherein the design and base pattern have an average lighttransmissivity of at least 1%.
 31. A panel as claimed in claim 1,wherein the design and base pattern have an average light transmissivityof greater than 3%.
 32. A panel as claimed in claim 1, wherein saiddesign is superimposed with said base pattern by projection from oneside of said panel, whereby said design is visible from said one side ofsaid panel and a mirror image of said design is visible from the otherside of said panel.
 33. An illuminated panel assembly, comprising: apanel comprising a sheet of colored or colorless transparent materialand a transparent or translucent design, said transparent or translucentdesign being superimposed with a base pattern which extends over thearea of said sheet covered by said design and being adhered to at leastone of said base pattern and said sheet of colored or colorlesstransparent material, said base pattern comprising a translucent baselayer and subdividing the panel into a plurality of areas of said baselayer and/or a plurality of areas of said colored or colorlesstransparent material, said layers being constructed and arranged suchthat the whole of said design is visible from a first viewing positionlocated on one side of the panel when a sufficiently high level ofillumination is provided on the other side of the panel and a mirrorimage of the whole of said design is visible from a second viewingposition located on the other side of the panel when a sufficiently highlevel of illumination is provided on said one side of the panel; and aspotlight source of illumination located on said other side of saidpanel, outside a prismatic space formed by a projection of said panelperpendicular to said panel and directed to illuminate said other sideof said panel; whereby the perceptibility of the design perceived by anobserver located at said first viewing position, with the spotlightsource of illumination shielded from the observer by an opaque materialdisposed between the observer and the spotlight source of illuminationsuch that the spotlight source of illumination is outside any directline of sight from the viewer, is substantially increased by shining thespotlight source of illumination on said other said of said panel.
 34. Amethod of displaying a transparent or translucent design, said methodcomprising: providing a panel comprising a sheet of colored or colorlesstransparent material having said transparent or translucent designprinted thereon, said transparent or translucent design beingsuperimposed with a base pattern which extends over the area of saidsheet covered by said design and being adhered to at least one of saidbase pattern and said sheet of colored or colorless transparentmaterial, said base pattern comprising a translucent base layer andsubdividing the panel into a plurality of areas of said base layerand/or a plurality of areas of said colored or colorless transparentmaterial, said layers being constructed and arranged such that the wholeof said design is visible from a first viewing position located on oneside of the panel when a sufficiently high level of illumination isprovided on the other side of the panel and a mirror image of the wholeof said design is visible from a second viewing position located on theother side of the panel when a sufficiently high level of illuminationis provided on said one side of the panel; and illuminating the panel onsaid other side of said panel with a first spotlight source ofillumination, said first spotlight source of illumination being locatedoutside a prismatic space formed by a projection of said panelperpendicular to said panel and said first spotlight source ofillumination being directed onto said other side of said panel.
 35. Amethod of displaying a transparent or translucent design as claimed inclaim 34, further comprising increasing the luminous intensity of saidfirst spotlight source illumination on said other side of said panel toincrease the luminance and perceptibility of said design from said firstviewing position.
 36. A method of displaying a transparent ortranslucent design as claimed in claim 35, said method furthercomprising controlling the perceptibility from said first viewingposition of said design and an object spaced from the other side of thepanel, opposite to said first viewing position and with said paneldisposed therebetween, by: a) illuminating the space on said other sideof the panel with a source of general illumination of sufficientluminous intensity such that, when said first spotlight source ofillumination is not switched on, said object forms a principal perceivedimage from said first viewing position; and b) switching on said firstspotlight source of illumination at a sufficient level of luminousintensity such that the principal perceived image from said firstviewing position changes from said object to said design.
 37. A methodof illuminating a panel as claimed in claim 36, said method furthercomprising selecting the level of illumination provided by each of theillumination sources whereby a principal perceived image visible at saidfirst viewing position alternates between said design and said object.38. A method of displaying a transparent or translucent design asclaimed in claim 34, said method further comprising a) variablyilluminating the panel on said other side of said panel with said firstspotlight source of illumination, b) variably illuminating the space onsaid other side of said panel with a first source of generalillumination, c) variably illuminating said one side of said panel witha second spotlight source of illumination directed onto said one side ofsaid panel, and/or d) variably illuminating the space on said one sideof said panel with a second source of general illumination.
 39. A methodof displaying a transparent or translucent design as claimed in claim38, said method further comprising selecting the level of illuminationprovided by each of the illumination sources such that 1) a firstobserver at said first viewing position on said one side of said panelcan optionally see both the design and a second observer at said secondviewing position on said other side of said panel; and 2) said secondobserver can optionally see both a mirror image of said design and saidfirst observer at said first viewing position on said one side of saidpanel.
 40. A method of illuminating a panel as claimed in claim 39, saidmethod further comprising increasing the luminous intensity of saidfirst source of general illumination until said second observer locatedat said second viewing position is visible to and forms the principalperceived image for said first observer located at said first viewingposition, and then increasing the luminous intensity of said firstspotlight source of illumination whereby said design becomes a principalperceived image for said first observer located at said first viewingposition.
 41. A method of illuminating a panel as claimed in claim 38,further comprising increasing the luminous intensity of said secondspotlight source of illumination until a mirror image of said design isvisible to an observer located at said second viewing position on saidother side of said panel.
 42. A method as claimed in claim 34, whereinsaid method comprises projecting said design onto said base layer usingsaid first spotlight source of illumination, whereby said design isvisible from said one side of said panel and a mirror image of saiddesign is visible from the other side of said panel.
 43. A panel asclaimed in claim 3, wherein all of said geometric elements have the sameshape.
 44. A panel as claimed in claim 1, wherein said design isvisually independent of said base pattern such that at least a part ofsaid design remains clearly perceptible to an observer on said one sideof said panel even when the observer has moved far enough away from saidpanel that individual elements of said base pattern no longer can beresolved by the eye of the observer.
 45. A panel as claimed in claimed1, wherein said base pattern comprises a perforated, transparentmaterial.
 46. A panel as claimed in claim 1, wherein said sheet ofcolored or colorless transparent material comprises a partiallymetallized mirror material.
 47. An illuminated panel assembly as claimedin claim 33, wherein a mirror material is spaced from the other side ofsaid panel.
 48. An illuminated panel assembly as claimed in claim 47,wherein said mirror material is a partially metallized mirror material.49. An illuminated panel assembly as claimed in claim 33, said assemblyfurther comprising a rear design panel that is spaced from the otherside of said panel and a second spotlight source of illumination that isdirected to illuminate said rear design panel.